中華民國內政部建築研究所中華民國內政部建築研究所

一、研究緣起
開發具有節能、環保及再利用等性質的混凝土已成為重要的課題，現行做法係以飛灰、爐石取代部分水泥拌製混凝土，以減少水泥的用量，並改善混凝土中的界面過渡區品質，增加混凝土的晚期強度及耐久性；骨材部分則以人造輕質骨材或再生骨材取代天然常重骨材，減緩開採天然砂石對環境的影響。水泥漿體與骨材間之交界區域稱為界面過渡區，此區為混凝土中的弱面，因此界面過渡區品質的好壞決定混凝土的強度及耐久性，而骨材吸水行為、膠結材料的種類則影響界面過渡區的品質，國內外已有相關研究探討該課題，惟對於膠結材料用量的影響或更進一步探討鋼筋與混凝土間的界面性質則付之闕如。
二、研究方法及過程
本研究規劃常重混凝土、輕質混凝土及再生混凝土等三種混凝土，設計抗壓強度為280kgf/cm2，飛灰及爐石取代水泥量分別為0%、30%、45%及60%，試驗項目包含抗壓試驗、抗彎試驗、鋼筋拉拔試驗、掃描式電子顯微鏡(SEM)觀測、混凝土滲透試驗及快速評估混凝土抵抗氯離子滲透能力試驗，探討膠結材料種類、用量及骨材種類對混凝土界面過渡區，以及與鋼筋間界面的影響。
三、重要發現
隨飛灰及爐石摻量的增加(如60%)，需添加較多的強塑劑及延長拌和時間，混凝土才具有流動性，因添加強塑劑致使混凝土凝結時間延後的現象也需注意。此外，摻有爐石之混凝土抗壓強度發展較摻有飛灰者理想，於早齡期即可提升混凝土的強度，並隨齡期的增加抗壓強度仍會持續提升；混凝土抗彎強度亦隨爐石摻量增加而提升。鋼筋拉拔試驗結果顯示，無摻加卜作嵐摻料之常重混凝土的握裹應力較高，再生混凝土次之，輕質混凝土最小；整體而言，摻有爐石之混凝土握裹應力較高，摻有飛灰者次之，無摻卜作嵐摻料者最小。混凝土滲透試驗及快速氯離子滲透試驗也顯示，隨飛灰或爐石摻量的增加，混凝土的滲透率降低，耐久性較好。掃描式電子顯微鏡觀測結果則顯示，隨著齡期的增加，三種常混凝土與鋼筋間界面的氫氧化鈣數量逐漸減少，可有效改善界面的品質，增加混凝土與鋼筋間的握裹應力。 
四、主要建議事項
根據卜作嵐材料混凝土與鋼筋間界面品質及握裹強度之研究成果，本研究提出下列具體建議。以下分別從立即可行建議及中長期建議加以列舉。
建議一
檢送本所摻加卜作嵐材料混凝土配比設計，提高混凝土抗壓強度及鋼筋握裹強度之相關混凝土配比設計研究成果供業界參採：立即可行之建議
主辦機關：台灣區預拌混凝土工業同業公會
本研究規劃常重、輕質及再生骨材混凝土等三種混凝土，設計抗壓強度為280kgf/cm2，飛灰及爐石之水泥取代量分別為0%、30%、45%及60%，試驗項目包含抗壓、抗彎、鋼筋拉拔試驗、掃描式電子顯微鏡(SEM)觀測、混凝土滲透試驗及快速評估混凝土抵抗氯離子滲透能力試驗，進而探討膠結材料種類、用量及骨材種類對混凝土界面過渡區，以及與鋼筋間界面的影響，根據試驗結果顯示，整體而言摻有爐石之混凝土抗壓強度發展較摻有飛灰者理想，於早齡期即可提升混凝土的強度，並隨齡期的增加抗壓強度仍會持續提升；混凝土抗彎強度亦隨爐石摻量增加而提升。鋼筋拉拔試驗結果顯示，無摻加卜作嵐摻料之常重骨材混凝土的握裹應力較高，再生骨材混凝土次之，輕質骨材混凝土最小；摻有爐石之混凝土握裹應力較高，摻有飛灰者次之，無摻加卜作嵐摻料者最小；混凝土滲透試驗及快速氯離子滲透試驗也顯示，隨飛灰或爐石摻量的增加，混凝土的滲透率降低，耐久性較好；另掃描式電子顯微鏡觀測結果則顯示，隨著齡期的增加，摻有卜作嵐摻料之混凝土與鋼筋間界面的氫氧化鈣數量逐漸減少，可有效改善界面的品質，增加混凝土與鋼筋間的握裹應力。本研究摻加飛灰及爐石等卜作嵐材料，提高混凝土抗壓強度及鋼筋握裹強度等之不同混凝土配比設計研究成果資料供業界參採。
建議二
建議後續可辦理卜作嵐摻料對混凝土界面微觀結構之相關研究，以助增加混凝土之抗壓強度及降低透水性，並減少粒料析離及梁柱接頭區鋼筋之埋置長度：中長期性建議
主辦機關：內政部建築研究所
本研究成果顯示，飛灰、爐石等卜作嵐材料取代部分水泥添加於混凝土中，在進行卜作嵐反應的過程會消耗混凝土與鋼筋間之水化產物氫氧化鈣，使混凝土緻密性增加，有助於提升混凝土晚期強度；另從握裹強度發展顯示，惟摻有飛灰之再生骨材混凝土，其握裹強度發展較無規律，主要原因是再生骨材表面孔隙量較多、吸水量大，加上卜作嵐反應的影響，使再生骨材混凝土與鋼筋間之界面過渡區趨於複雜，建議後續可辦理卜作嵐摻料對混凝土界面微觀結構之相關研究，以助增加混凝土之抗壓強度及降低透水性，並減少粒料析離及梁柱接頭區鋼筋之埋置長度。

1.Purpose of Research
The development of concrete with energy conservation, environmental protection and reuse has become an important issue. The current practice is to replace partial cement with fly ash and blast slag fume to reduce cement, improve interfacial transition zone in concrete, increase the strength at late age and durability of concrete; use lightweight aggregate or recycled aggregatethe to replace normal-weight aggregate to slow down the environmental impact of mining natural aggregate. The boundary area between cement paste and aggregate is defined as the interfacial transition zone. This zone is a weak area of the concrete. Therefore, the interfacial transition zone determines the strength and durability of concrete, while the absorption of water by aggregate and the kinds of cementitious materials affect the quality of interfacial transition zone. Some researches already discuss the interfacial transition zone of concrete, however there is few research invesitgate the amount of cementitious materials on the interfacial properties between reinforcing bar and concrete.
2.Methodology and Process
The study aims to invesitgate the kinds of aggregates, the amount of Pozzonalic materials on the interfacial properties between reinforcing bar and concrete. There are three kinds of concrete adopted, such as normal-weight concrete, lightweight concrete and recycled concrete. The designed compressive strength is 280kgf/cm2, and the replacement rates of fly ash and blust slag fume are 0%, 30%, 45% and 60%, respectively. The experimental items include the tests of compressive strength, flexural strength, pull-out of reinforcing bar, scanning electron microscope (SEM), water permeability and rapid chloride permeability and son.    
3.Important Findings
With the increase of the replacement rate of fly ash and blust slag fume (such as 60%), it is necessary to add more superplasticizer and extend the mixing time to keep the workability of concrete.  Add too much superplasticizer inducing the delaying setting time of concrete is also required to be noted. In addition, the compressive strength of concrete incorporating blust slag fume is better than that of fly ash. Adding blust slag fume can make concrete enhance compressive strength at early age, and the strength still continue to increase with the increase of age. The flexural strength of concrete also increases with the increase in replacement rate of blus slag fume. The results of the pull-out test show that the normal-weight concrete without adding Pozzonzlic materials is higher than those of recycled concrete and lightweight concrete. Overall, the concrete with blus slag fume has a better bond strength, the concrete with fly ash is inferior and the concrete without pozzomalic materials has the lowest bond srength. The water permeability test and the rapid chloride ion permeation test also showed that the permeability of concrete decreased with the increase of the blast slag fume, resulting the concrete has a better durability. The observation result of scanning electron microscope shows that the amount of calcium hydroxide at the interface between the concrete and reinforcing bar gradually decreases with the age increasing, which can effectively improve the bond stress between the concrete and reinforcing bar.
4.Major Recommedations
1)Immediate implementation: 
Sponsor Agency: Taiwan Ready-mixed Concrete Industry Association
Co-sponsor Agency: Architecture and Building Research Institute, Ministry of the Interior
The results of the research show that the replacement rate of Pozzolanic materials exceeds 30% of the weight of cement, concrete will delay the setting time. This problem can be overcome by the mix design of concrete and improving the performance of superplasticizer, which making the final setting time of concrete within 24 hours to avoid affecting the early strength of the concrete. However, the superplasticizer researchers do not understand the basic properties of fly ash and slag fume well, especially the properties of the overall cementitious materials at high content. They need to cooperate with civil materials engineeringers to develop superplasticizers suitable for concrete incorporating high volume Pozzonalic materials.
2)Long-term implementation: 
Sponsor Agency: Architecture and Building Research Institute,Ministry of the Interior
The results of the research show that Pozzonalic materials can improve the bond strength between concrete and reinforcing bar and   the failure type of concrete is splitting and brittle failure. However, this result can't present the flexural failure and bond strength of reinforcement concrete beams. It is necessary to further invesitgate the influence of Pozzonalic materials on the bond strength of reinforced concrete beams. Using the flexure bond test of reinforcement concrete beams and the observation of the ITZ microstructure to research the reaction mechanism of Pozzonalic materials on the bond strength of reinforcement concrete beams. The study result can be applied in the desing of this concrete.